EP0089264B1 - Method and device for generating synchronizing signals in an optical recording-reproducing apparatus for record carriers - Google Patents

Method and device for generating synchronizing signals in an optical recording-reproducing apparatus for record carriers Download PDF

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Publication number
EP0089264B1
EP0089264B1 EP83400428A EP83400428A EP0089264B1 EP 0089264 B1 EP0089264 B1 EP 0089264B1 EP 83400428 A EP83400428 A EP 83400428A EP 83400428 A EP83400428 A EP 83400428A EP 0089264 B1 EP0089264 B1 EP 0089264B1
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EP
European Patent Office
Prior art keywords
digital data
transitions
sites
substrate
transcription
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Expired
Application number
EP83400428A
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German (de)
French (fr)
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EP0089264A1 (en
Inventor
Jean-Louis Gerard
Jean-Claude Lehureau
Marc Loret
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Thales SA
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Thomson CSF SA
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B27/00—Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
    • G11B27/10—Indexing; Addressing; Timing or synchronising; Measuring tape travel
    • G11B27/19—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/16—Digital recording or reproducing using non self-clocking codes, i.e. the clock signals are either recorded in a separate clocking track or in a combination of several information tracks
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B27/00—Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
    • G11B27/10—Indexing; Addressing; Timing or synchronising; Measuring tape travel
    • G11B27/19—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier
    • G11B27/24—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier by sensing features on the record carrier other than the transducing track ; sensing signals or marks recorded by another method than the main recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B27/00—Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
    • G11B27/10—Indexing; Addressing; Timing or synchronising; Measuring tape travel
    • G11B27/19—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier
    • G11B27/28—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier by using information signals recorded by the same method as the main recording
    • G11B27/30—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier by using information signals recorded by the same method as the main recording on the same track as the main recording
    • G11B27/3027—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier by using information signals recorded by the same method as the main recording on the same track as the main recording used signal is digitally coded
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0045—Recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/005—Reproducing
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B2220/00—Record carriers by type
    • G11B2220/20—Disc-shaped record carriers

Definitions

  • the present invention relates to a method for generating synchronization signals used in an apparatus for optical transcription of data on an information medium, during the writing and / or reading phases, in particular of digital data recorded on a disc. . It also relates to an optical device for implementing this method.
  • this information is recorded in the form of microreliefs along tracks having the configuration of spiral or concentric circles, this latter configuration being the most used when it is a question of recording the digital data. In particular, it facilitates random access to recorded data as well as recording divided into blocks or sectors.
  • a first method in so-called multitrack systems, at least one other track is associated with each track reserved for the recording of useful information along which various information is recorded and in particular clock signals allowing the synchronization of the reading useful information.
  • the tracks intended for synchronization are pre-etched and have regularly spaced disturbances optically detectable.
  • a first beam is focused on the useful information track used to read this information, and a second beam, separate but in constant mechanical coupling relation with the first, is used to read synchronization information.
  • a second variant single beam reads the two pieces of information. In this case, it is necessary that the two types of information can be easily discriminated.
  • the frequency spectra associated with this information can be different.
  • the pre-engraved synchronization information can also be used during the writing phase. It is known from document EP-A-0032271 an information medium corresponding to the second variant mentioned above but whose reading implements the exploration of the track with two beams whose impact points are set back l 'one over the other. Provision is made for phase adjustment of a clock signal read by the first beam with a portion of the clock signal read by the second beam.
  • the synchronization clock signals can be derived from reading the information itself.
  • the microreliefs have two reference levels, associated with the logical values "0" and "1" respectively.
  • the synchronization signals are derived from the detection of transitions from one determined level to the other and are used to slave in frequency and in phase an oscillator, conventionally of the voltage control type (known by the acronym VCO, from the Anglo-Saxon expression “Voltage controlled oscillator”) fitted with a phase lock feedback loop (PLL: "phase lock loop”).
  • VCO voltage control type
  • PLL phase lock feedback loop
  • special bursts of recorded pulses are used to initialize the servo.
  • this type of coding does not allow a maximum recording density. It is also known to increase this density, to use non-self-synchronizing codes for example the code N.R.Z. (not return to zero).
  • the characteristic of this type of code is that it does not have a transition from one bit of information to another if these two bits remain at the same logical value. It is therefore more difficult to derive, from reading the information thus coded, the signals necessary for synchronization.
  • the present invention proposes to overcome the drawbacks of the known art while retaining the possibility of a maximum recording density.
  • the method of the invention consists in placing along the tracks, regularly or not, recorded elements used for synchronization or flags. Naturally these flags must be "transparent" to the electronic circuits responsible for detecting and processing useful information. These synchronization samples serve to resynchronize each time a flag is passed under a read head, the circuits generating synchronization signals.
  • the invention also relates to a device for implementing such a method and the information medium particularly suitable for this method.
  • the methods of recording information on an optical disc are well known.
  • the disc has at least one layer, generally superficial, of material sensitive to certain types of radiation.
  • a beam generated by a laser source is focused on this layer of material and microreliefs are created along the tracks by thermooptic effect. These tracks can be virtual, that is to say created at the time of data entry, or even be pre-engraved in any form.
  • Methods of reading information and tracking are also well known. Generally used for tracking, either a second reading beam, or the beam used for writing; or the same beam is used for all functions. The interaction of this beam with the microreliefs scrolling under a read head creates interference orders which are detected by optoelectronic detection means.
  • Reading can be done either by transmission through the disc and detection using photodetector cells placed near the underside of the disc, or by reflection of the radiation on the disc and reverse return of the light taken up by systems.
  • optical systems comprising mirrors directing the reflected beams towards photodetector cells.
  • the photodetector cells can also be used to ensure correct focusing of the reading beam on the recorded face. Finally, these cells are used to generate electrical signals representing the recorded information.
  • the microreliefs are in the form of alterations along the tracks associated with two well defined levels and separated by transitions between these two levels. Interpiste zones are uniform zones whose surface is at one of these levels.
  • the detection means will translate these level variations by a series of pulses also having two states which can be associated with logic states "0" and "1" and having more or less abrupt transitions between these two states.
  • the subject of the invention is a method the main characteristic of which is to derive the signals necessary for synchronizing the writing and / or reading of digital data on an optical information medium, of digital data specific or flags, recorded on the track common to digital information data, but spatially multiplexed with it.
  • flags can be registered prior to any registration of useful information and are then used for the generation of synchronization signals during the subsequent registration of this information and during successive readings; or are multiplexed in time with the recording of this information and are used when reading it later.
  • FIG. 2 illustrates an example of an arrangement in accordance with the invention.
  • flags 92 are recorded in accordance with the main feature of the invention.
  • Such a pulse is illustrated by the diagram in FIG. 3.
  • a first part is at logic "1" during the time interval equal to 1.5 T, time interval T A -T B and at logic "0" during the time interval equal to T: interval Ta-Tc.
  • the disc is pre-burned, that is to say contains the flags, registered prior to any recording of digital data of useful information.
  • the registration of these flags along the tracks is periodic and the spaces left free between the defined flags are blocks or data sectors: in this case it is possible to obtain a fully synchronous operating mode.
  • the second case is that where the flags are registered at the same time as the recording of the digital data of useful information.
  • the flags can be registered in specific sites, regularly spaced or not, or even be registered multiplexed with the digital data of useful information.
  • Optoelectronic detection members and the associated electronic circuits 1 provide a read signal V L transmitted on the one hand to conventional circuits for processing the information read 6 and, on the other hand, to the specific circuits of the present invention.
  • the method of the invention it is first of all necessary to determine whether the signals V L come from the reading of useful information or on the contrary from the reading of flags intended for synchronization. This step is carried out using circuits. 2 flags detection which will be detailed later. These circuits supply an authorization signal VA transmitted to phase shift calculation circuits 3.
  • the purpose of these circuits is to supply information A (p representative of the time of appearance d 'a transition from a determined direction of the microrelief scrolling under the reading spot.
  • the authorization signal VA for example after logic inversion VA by the inverter 7, can be used for the purpose of inhibiting-authorizing the operation of the processing circuits for the information read 6.
  • the device also includes clock circuits 4 generating synchronization pulses H regenerated by circuits 5, that is to say re-phased and transmitted in the form of a re-synchronized signal H s to the processing circuits of the information read.
  • Clock circuits also supply to the phase shift calculation circuit 3 reference clock signals H, and the signals H.
  • these clock circuits comprise an oscillator controlled by quartz having great stability.
  • the frequency and the phase of the synchronization signals H s are generated from the phase information extracted from the detected flags.
  • the bit rate is regenerated, that is to say the frequency of the clock H from the block rhythm, that is to say at the rate of the detection of flags (successive passages under the read head).
  • the signal VA is also transmitted to the clock circuits 4.
  • the resetting by the circuits 5 is carried out using the information ⁇ provided by the flag detection circuits 2.
  • the bit rate of the digital data of useful information read is very stable, that is to say if the phase shift per block (between two passages of flags) is less than a fraction of binary element ( slip in time less than a determined fraction of the time interval T) the frequency regeneration operation is not necessary.
  • the device of the invention is reduced to the simplified circuits illustrated in FIG. 5.
  • the authorization-inhibition signals can be derived from the clock signals, respectively H A and via the inverter 8: H A.
  • the other circuits are identical to those of FIG. 4 and will not be described again.
  • FIG. 6 An example of a circuit for detecting flags and determining the instant when a flag passes under the reading spot is illustrated in FIG. 6.
  • This circuit comprises a first circuit 20 for shaping the signal read V L - It can advantageously consist of a bistable element comparing a read signal V L with a threshold voltage V THRESHOLD supplying a pulse V LS , for example, in a logic state "1" when the signal read exceeds the threshold and with l 'state "0" otherwise.
  • This signal V Ls is transmitted to a circuit 21 intended to generate a pulse signal defining a time window V F.
  • the curve H represents pulses supplied by the clock circuits 4 of basic duration T.
  • the pulse signal V LS can have a phase shift with respect to any clock signals modulo the period of these signals.
  • Circuit 21 is triggered by the rising amount of the first flag pulse, at time T A on the diagram, and delivers a pulse VF whose center is delayed by 1.5 T.
  • two flip-flops can be used monostable generating pulses of durations respectively slightly greater and slightly less than 1.5 T. The logical intersection of these two pulses can be used to determine the time window V F.
  • the phase shift information ⁇ can be obtained by comparison with a determined instant of the period of the basic clock signal H, digitally or analogically.
  • the signal ⁇ produced by the phase shift calculation circuits can be in the form of a pulse signal having a transition of a determined direction whose time of appearance is representative of the phase shift of the flag with respect to a predetermined time of the H clock signals or a binary address word defining the phase shift.
  • the clock signal H and a clock signal H R of frequency multiple of the repetition frequency of the basic clock signal H and in fixed phase relation with this signal are used.
  • the second clock signal can be easily derived from the H signal using a frequency multiplier.
  • the clock signal H R has a repetition frequency sixteen times greater than that of the signal H. It therefore defines sixteen sub-intervals.
  • a decoder circuit can supply a binary word ⁇ representing the offset of the instant T B with respect to a fixed reference instant of the period of the basic clock signal H, this modulo sixteen.
  • the binary word ⁇ or control word is used to reset the clock signal used as synchronization signal H s with each passing of the flag.
  • This signal can be used during the reading of digital data of useful information between the successive passages of two flags, that is to say, when these flags are registered before the recording of data, in the form of pre-engravings, also for the writing of these data.
  • the new regenerated clock signals must be in constant phase relation with the passage of the flags, that is to say for example with the instant T B falling edge of the flag pulse as it has just been determined.
  • the synchronization signals H s have the same frequency as the clock signals H and a phase relationship depending on the value of the control word ⁇ .
  • FIG. 7 An exemplary embodiment of the clock circuits is shown in FIG. 7.
  • These circuits include a conventional quartz-controlled oscillator, of the voltage-controlled type (“VCO”) provided with a phase-locked feedback loop (“ PLL ”) comprising in series a frequency divider 41 by a determined number N, a phase comparator 42 receiving on a first input the output of the divider 41 and on a second input the signals VA coming from the flag detector 2 and a low-pass filter 43.
  • the output frequency H of the oscillator is controlled on a multiple N of the rate at which flags pass. under the reading spot.
  • the oscillator which has just been described applies more particularly to the circuits illustrated in FIG. 4.
  • the oscillator can be reduced to its simplest expression, the phase comparison n being no longer necessary.
  • a clock signal H of frequency multiple of the basic clock signal H can be generated from the latter using a frequency multiplier 44.
  • the phase-resetting circuits 5 can also include a voltage-controlled oscillator provided with a phase-locked loop of the type which has just been described, controlled in frequency by the clock signals H or a programmable delay line .
  • the phase adjustment on the flags is done using the control signal ⁇ .
  • FIG. 9 schematically illustrates a recording-reading apparatus on a medium by optical means in which the method of the present invention can be implemented.
  • a disk 90 rotating in a plane XOY around an axis parallel to the third axis Z of the reference triede XYZ has on its upper face a layer of heat-sensitive material in which information has been recorded along the tracks 91.
  • These tracks also include flags 92 associated with a specific code in accordance with what has been described.
  • the useful information digital data is recorded between these flags in zones 93, preferably of constant length.
  • the disc with a diameter of about 30 cm, is driven by a rotational movement communicated by a drive motor secured to the chassis of the optical recording-reading system.
  • the tracks for example 40,000 in number, are inscribed inside a crown centered on the axis of rotation and of width equal to approximately 8 cm.
  • the number of flags registered per concentric circular tracks must be sufficient to overcome parasitic phenomena related to the nature of the support or to the fluctuation of the speed of rotation. Typically 3,500 flags are entered per runway, taking into account the previous data.
  • the device for accessing a predetermined track of the disc comprises a fixed part comprising an energy source (not shown) generating a beam of parallel rays f and a mobile part constituted by the recording-playback head itself.
  • the latter comprises a microscope type objective O b , integral with an electromagnetic coil B moving in the magnetic field of a permanent magnet (not shown) ensuring vertical servo-control or focusing and a galvanometric mirror M 1 ensuring the radial control.
  • the galvanometric mirror M 1 is movable around an axis Ay parallel to the axis OY of the reference triede so as to ensure said radial control.
  • the beam f is focused in a tacheta at a determined location on the disc on one of the tracks 91 mentioned above. It is assumed here that the system is of the single-beam-single track type, that is to say a system in which the single beam f is used alternately for writing and reading as well as for ensuring the functions of radial tracking of track and focusing. . This aspect is outside the scope of the invention.
  • a semi-transparent plate M 2 is interposed, for example, on the path of the single beam f.
  • the beam reflected by the disc is then detected by photodetector means D which generate the signal V L to circuits 94 for processing this signal.
  • These circuits include in particular circuits specific to the invention, for example the device described in relation to FIG. 7.
  • the invention is also compatible with recording-reading apparatuses using more than one beam, for example a reading beam and a writing beam.
  • the method of the invention makes it possible, among other advantages, to take advantage of the independence which exists between the coding of digital data representing the information and the synchronization as well as a less dependence with respect to the losses of information due to "blanks" in reading better known by the Anglo-Saxon name of "dropouts".

Description

La présente invention se rapporte à un procédé de génération de signaux de synchronisation utilisés dans un appareil de transcription optique de données sur un support d'information, pendant les phases d'écriture et/ou de lecture, notamment de données numériques enregistrées sur un disque. Elle concerne également un dispositif optique de mise en oeuvre de ce procédé.The present invention relates to a method for generating synchronization signals used in an apparatus for optical transcription of data on an information medium, during the writing and / or reading phases, in particular of digital data recorded on a disc. . It also relates to an optical device for implementing this method.

Les méthodes d'enregistrement sont bien connues de l'homme de métier et sortent du cadre de la présente invention. Le plus souvent, ces informations sont enregistrées sous forme de microreliefs le long de pistes ayant la configuration de spirale ou de cercles concentriques, cette dernière configuration étant la plus usitée lorsqu'il s'agit d'enregistrer les données numériques. Elle facilite notamment l'accès aléatoire à une donnée enregistrée ainsi qu'un enregistrement divisé en blocs ou secteurs.The recording methods are well known to those skilled in the art and are outside the scope of the present invention. Most often, this information is recorded in the form of microreliefs along tracks having the configuration of spiral or concentric circles, this latter configuration being the most used when it is a question of recording the digital data. In particular, it facilitates random access to recorded data as well as recording divided into blocks or sectors.

Lors de la lecture, quelle que soit la méthode d'enregistrement, il est nécessaire de disposer de signaux permettant la synchronisation de cette lecture. Pour ce faire, de nombreuses méthodes sont également connues.During the reading, whatever the recording method, it is necessary to have signals allowing the synchronization of this reading. To do this, many methods are also known.

Selon une première méthode, dans les systèmes dits multipistes, à chaque piste réservée à l'enregistrement d'information utile est associée au moins une autre piste le long de laquelle sont enregistrées diverses informations et notamment des signaux d'horloge permettant la synchronisation de la lecture de l'information utile. Dans une variante de réalisation, les pistes destinées à la synchronisation sont prégravées et comportent des perturbations régulièrement espacées décelables optiquement. Lors de la lecture, dans une première variante (système multifaisceau), un premier faisceau est focalisé sur la piste d'information utile utilisé pour lire ces informations, et un second faisceau, séparé mais en relation de couplage mécanique constant avec le premier, est utilisé pour lire les informations de synchronisation. Dans une seconde variante, (système monofaisceau) un seul faisceau lit les deux informations. Dans ce cas, il est nécessaire que les deux types d'informations puissent être aisément discriminés. A titre d'exemple, les spectres de fréquences associés à ces informations peuvent être différents. Dans cette variante les informations de synchronisation prégravées peuvent également être utilisées pendant la phase d'écriture. Il est connu du document EP-A-0032271 un support d'information correspondant à la seconde variante mentionnée ci- dessus mais dont la lecture met en oeuvre l'exploration de la piste avec deux faisceaux dont les points d'impact sont en retrait l'un par rapport à l'autre. Il est prévu le recalage en phase d'un signal d'horloge lu par le premier faisceau avec une portion du signal d'horloge lu par le second faisceau.According to a first method, in so-called multitrack systems, at least one other track is associated with each track reserved for the recording of useful information along which various information is recorded and in particular clock signals allowing the synchronization of the reading useful information. In an alternative embodiment, the tracks intended for synchronization are pre-etched and have regularly spaced disturbances optically detectable. When reading, in a first variant (multibeam system), a first beam is focused on the useful information track used to read this information, and a second beam, separate but in constant mechanical coupling relation with the first, is used to read synchronization information. In a second variant, (single-beam system) a single beam reads the two pieces of information. In this case, it is necessary that the two types of information can be easily discriminated. For example, the frequency spectra associated with this information can be different. In this variant, the pre-engraved synchronization information can also be used during the writing phase. It is known from document EP-A-0032271 an information medium corresponding to the second variant mentioned above but whose reading implements the exploration of the track with two beams whose impact points are set back l 'one over the other. Provision is made for phase adjustment of a clock signal read by the first beam with a portion of the clock signal read by the second beam.

Pour augmenter la densité d'enregistrement possible, il a été également proposé d'utiliser une seule piste. Dans ce cas, les signaux d'horloge de synchronisation peuvent être dérivés de la lecture de l'information elle-même.To increase the possible recording density, it has also been proposed to use a single track. In this case, the synchronization clock signals can be derived from reading the information itself.

Pour rendre plus aisée la synchronisation, on utilise classiquement des codes dits auto-synchronisants ou à maximum de transitions, quelque soit le contenu de l'information source à enregistrer. En effet, de façon pratique, les microreliefs présentent deux niveaux de référence, associés aux valeurs logiques "0" et "1" respectivement. Les signaux de synchronisation sont dérivés de la détection des transitions d'un niveau déterminé à l'autre et sont utilisés pour asservir en fréquence et en phase un oscillateur, classiquement de type à commande en tension (connu sous le sigle V.C.O., de l'expression anglo-saxonne "Voltage controlled oscillator") munie d'une boucle de rétroaction à verrouillage de phase (P.L.L.: "phase lock loop"). En outre, des salves spéciales d'impulsions enregistrées sont utilisées pour initialiser l'asservissement.To make synchronization easier, conventionally so-called self-synchronizing codes or codes with maximum transitions are used, whatever the content of the source information to be recorded. In practice, the microreliefs have two reference levels, associated with the logical values "0" and "1" respectively. The synchronization signals are derived from the detection of transitions from one determined level to the other and are used to slave in frequency and in phase an oscillator, conventionally of the voltage control type (known by the acronym VCO, from the Anglo-Saxon expression "Voltage controlled oscillator") fitted with a phase lock feedback loop (PLL: "phase lock loop"). In addition, special bursts of recorded pulses are used to initialize the servo.

Cependant ce type de codage ne permet pas une densité maximale d'enregistrement. Il est également connu pour augmenter cette densité, d'utiliser des codes non auto-synchronisants per exemple le code N.R.Z. (non retour à zéro). Ce type de code a pour caractéristique de ne pas présenter de transition d'un bit d'information à l'autre si ces deux bits restent à la même valeur logique. Il est alors plus difficile de dériver, de la lecture de l'information ainsi codée, les signaux nécessaires à la synchronisation.However, this type of coding does not allow a maximum recording density. It is also known to increase this density, to use non-self-synchronizing codes for example the code N.R.Z. (not return to zero). The characteristic of this type of code is that it does not have a transition from one bit of information to another if these two bits remain at the same logical value. It is therefore more difficult to derive, from reading the information thus coded, the signals necessary for synchronization.

La présente invention se propose de pallier les inconvénients de l'art connu tout en conservant la possibilité d'une densité maximale d'enregistrement. Pour ce faire, le procédé de l'invention consiste à disposer le long des pistes, régulièrement ou non, des éléments enregistrés utilisés pour la synchronisation ou drapeaux. Naturellement ces drapeaux doivent être "transparents" aux circuits électroniques chargés de détecter et de traiter les informations utiles. Ces échantillons de synchronisation servent à resynchroniser à chaque passage d'un drapeau sous une tête de lecture les circuits générateurs de signaux de synchronisation.The present invention proposes to overcome the drawbacks of the known art while retaining the possibility of a maximum recording density. To do this, the method of the invention consists in placing along the tracks, regularly or not, recorded elements used for synchronization or flags. Naturally these flags must be "transparent" to the electronic circuits responsible for detecting and processing useful information. These synchronization samples serve to resynchronize each time a flag is passed under a read head, the circuits generating synchronization signals.

L'invention a donc pour objet un procédé de génération de signaux de synchronisation dans un appareil de transcription optique de données numériques sur un support animé d'un mouvement d'exploration; lesdites données étant enregistrées sous forme de perturbations d'au moins une couche de matériau du support, optiquement détectables le long de pistes de configuration déterminée; lesdites pistes comportant une succession de sites non-contigus dédiés au stockage desdites données entre lesquels sont intercalés des sites dédiés à un autre usage; ledit appareil comportant des moyens pour focaliser en une tache d'exploration, au moins un faisceau d'énergie lumineuse sur une desdites pistes, des moyens optoélectroniques de détection de l'interaction de ce faisceau avec lesdites perturbations défilant sous la tache d'exploration et des moyens sélecteurs reliés à ces moyens optoélectriques pour délivrer un signal caractéristique du contenu desdits sites intercalaires; procédé caractérisé en ce qu'il comprend les étapes suivantes:

  • -inscription exclusivement dans lesdits sites intercalaires de données numériques spécifiques sous forme d'une suite de perturbations de ladite couche de matériau produisant des transitions jouant le rôle de référence par rapport auxdits signaux de synchronisation mais dont les écarts sont discernables de ceux mis en ouvre pour la transcription desdites données numériques;
  • -génération locale, à l'extérieur du support, d'un signal périodique d'horloge comportant un élément définissant un instant de référence à mettre en rapport avec la transcription desdites données.
  • -identification sélective des données numériques spécifiques par lesdits moyens sélecteurs.
  • -détermination par lesdits moyens sélecteurs de l'instant de référence (TB) issu de l'exploitation d'une transition dont la sélection est commandée avec un retard déterminé par rapport à une autre transition; ladite transition et l'autre transition étant produites par la même perturbation inclue dans lesdites données numériques spécifiques (92) en réponse à l'exploration par ladite tache (ta) desdits sites intercalaires, ledit retard dépendant de la durée estimée existant entre ces deux transitions.
  • -détermination du décalage de cet instant de référence avec l'instant de référence propre audit signal périodique d'horloge;
  • -et génération d'un signal de synchronisation à partir dudit signal périodique d'horloge corrigé en phase proportionnellement audit décalage.
The subject of the invention is therefore a method of generating synchronization signals in an optical transcription apparatus for digital data on a support animated by an exploration movement; said data being recorded in the form of disturbances of at least one layer of support material, optically detectable along tracks of determined configuration; said tracks comprising a succession of non-contiguous sites dedicated to the storage of said data between which are interspersed sites dedicated to another use; said apparatus comprising means for focusing into an exploration spot, at least one light energy beam on one of said tracks, optoelectronic means for detecting the interaction of this beam with said disturbances traveling under the exploration spot and selector means connected to these optoelectric means for delivering a signal characteristic of the content of said intermediate sites; process characterized in that it comprises the following stages:
  • -inclusion exclusively in said intermediate sites of specific digital data in the form of a series of disturbances of said layer of material producing transitions playing the role of reference with respect to said synchronization signals but the deviations of which are discernible from those implemented for transcribing said digital data;
  • -local generation, outside the support, of a periodic clock signal comprising an element defining a reference instant to be linked with the transcription of said data.
  • - selective identification of specific digital data by said selector means.
  • determination by said selector means of the reference instant (T B ) resulting from the exploitation of a transition whose selection is controlled with a delay determined with respect to another transition; said transition and the other transition being produced by the same perturbation included in said specific digital data (92) in response to the exploration by said spot (ta) of said intermediate sites, said delay depending on the estimated duration existing between these two transitions .
  • determination of the offset of this reference instant with the reference instant proper to said periodic clock signal;
  • and generation of a synchronization signal from said periodic clock signal corrected in phase in proportion to said offset.

L'invention a encore pour objet un dispositif de mise en oeuvre d'un tel procédé et le support d'information particulièrement adapté à ce procédé.The invention also relates to a device for implementing such a method and the information medium particularly suitable for this method.

L'invention sera mieux comprise à l'aide de la description qui suit en référence aux figures annexées et parmi lesquelles:

  • -la figure 1 illustre deux types de codes mis en oeuvre pour le codage d'un même mot binaire;
  • -la figure 2 illustre schématiquement la configuration d'une piste d'un support d'information conforme à l'invention;
  • -la figure 3 est un diagramme illustrant un code particulier mis en oeuvre dans une variante préférée de l'invention;
  • -les figures 4 et 5 sont des diagrammes synoptiques de dispositifs selon deux variantes d'exécution de l'invention;
  • -les figures 6 et 7 représentent de façon plus détaillée certains éléments de ces dispositifs;
  • -la figure 8 est un diagramme sur lequel sont représentés des signaux les plus significatifs du fonctionnement du dispositif selon l'invention et leurs interrelations temporelles.
  • -la figure 9 représente schématiquement un appareil optique d'enregistrement-lecture dans lequel le dispositif de l'invention peut être mis en oeuvre.
The invention will be better understood with the aid of the description which follows with reference to the appended figures and among which:
  • FIG. 1 illustrates two types of codes used for coding the same binary word;
  • FIG. 2 schematically illustrates the configuration of a track of an information medium in accordance with the invention;
  • FIG. 3 is a diagram illustrating a particular code implemented in a preferred variant of the invention;
  • FIGS. 4 and 5 are block diagrams of devices according to two alternative embodiments of the invention;
  • FIGS. 6 and 7 show in more detail certain elements of these devices;
  • FIG. 8 is a diagram on which are represented the most significant signals of the operation of the device according to the invention and their temporal interrelations.
  • FIG. 9 schematically represents an optical recording-reading apparatus in which the device of the invention can be implemented.

Les procédés d'inscription d'informations sur un disque optique sont bien connus. Habituellement le disque comporte au moins une couche, généralement superficielle, en matériau sensible à certains types de radiations. Selon un des procédés les plus connus, lors de l'inscription, on focalise un faisceau généré par une source laser sur cette couche de matériau et on crée par effet thermooptique des microreliefs le long des pistes. Ces pistes peuvent être virtuelles, c'est à dire être créées au moment de l'inscription des données, ou encore être prégravées sous quelque forme que ce soit. Les procédés de lecture des informations et de suivi de piste sont également bien connus. On utilise généralement pour le suivi de piste, soit ün second faisceau de lecture, soit le faisceau ayant servi à l'écriture; ou encore le même faisceau sert pour toutes les fonctions. L'interaction de ce faisceau avec les microreliefs défilant sous une tête de lecture crée des ordres d'interférences qui sont détectés par des moyens optoélectroniques de détection. La lecture peut se faire, soit par transmission au travers du disque et détection à l'aide de cellules photodétectrices placées à proximité de la face inférieure du disque, soit par reflexion du rayonnement sur le disque et retour inverse de la lumière reprise par des systèmes optiques comprenant des miroirs dirigeant les faisceaux réfléchis vers des cellules photodétectrices.The methods of recording information on an optical disc are well known. Usually the disc has at least one layer, generally superficial, of material sensitive to certain types of radiation. According to one of the best known methods, during the registration, a beam generated by a laser source is focused on this layer of material and microreliefs are created along the tracks by thermooptic effect. These tracks can be virtual, that is to say created at the time of data entry, or even be pre-engraved in any form. Methods of reading information and tracking are also well known. Generally used for tracking, either a second reading beam, or the beam used for writing; or the same beam is used for all functions. The interaction of this beam with the microreliefs scrolling under a read head creates interference orders which are detected by optoelectronic detection means. Reading can be done either by transmission through the disc and detection using photodetector cells placed near the underside of the disc, or by reflection of the radiation on the disc and reverse return of the light taken up by systems. optical systems comprising mirrors directing the reflected beams towards photodetector cells.

Outre le suivi radial, les cellules photodétectrices peuvent également être utilisées pour assurer une focalisation correcte du faisceau de lecture sur la face enregistrée. Enfin, ces cellules sont utilisées pour générer des signaux électriques représentant l'information enregistrée.Besides the radial tracking, the photodetector cells can also be used to ensure correct focusing of the reading beam on the recorded face. Finally, these cells are used to generate electrical signals representing the recorded information.

Pour les applications dans le domaine de l'informatique, il est nécessaire du pouvoir enregistrer des données de type numérique de façon aléatoire à un endroit quelconque du disque. De même, lors de la lecture, l'accès aléatoire à ces informations est également requis. Une autre exigeance soulevée par ce type de dispositif est que la lecture doit être synchronisée sur l'éctriture. Or pour de nombreuses raisons dûes à des phénomènes parasites tels que des fluctuations de vitesse, une horloge extérieure ne peut suffir à cette fin. Les signaux de synchronisation doivent donc être dérivés directement des données enregistrées de façon à avoir une corrélation entre les données lues et les données inscrites.For computer applications, it is necessary to be able to record digital data at random anywhere on the disc. Likewise, when reading, random access to this information is also required. Another requirement raised by this type of device is that reading must be synchronized with writing. However for many reasons due to parasitic phenomena such as speed fluctuations, an external clock cannot be sufficient for this purpose. The synchronization signals must therefore be derived directly from the recorded data so as to have a correlation between the data read and the data recorded.

De façon pratique, les microreliefs se présentent sous forme d'altérations le long des pistes associés à deux niveaux bien définis et séparées par des transitions entre ces deux niveaux. Les zones interpistes sont des zones uniformes dont la surface est à l'un de ces niveaux. Les moyens de détection vont traduire ces variations de niveaux par une suite d'impulsions également présentant deux états qui peuvent être associées à des états logiques "0" et "1" et présentant des transitions plus ou moins brusques entre ces deux états.In practice, the microreliefs are in the form of alterations along the tracks associated with two well defined levels and separated by transitions between these two levels. Interpiste zones are uniform zones whose surface is at one of these levels. The detection means will translate these level variations by a series of pulses also having two states which can be associated with logic states "0" and "1" and having more or less abrupt transitions between these two states.

Dans l'art connu, il est d'usage de dériver des signaux de synchronisation de l'apparition d'une de ces transitions, par exemple un front montant ou un front descendant.In the known art, it is customary to derive synchronization signals from the appearance of one of these transitions, for example a rising edge or a falling edge.

Pour ce faire, on met classiquement en oeuvre des codes dits autosynchronisants ou du moins présentant un maximum de transitions, comme il a été rappelé.To do this, we classically implement so-called self-synchronizing codes or at least presenting a maximum of transitions, as has been recalled.

Cependant lorsqu'on désire augmenter la densité d'enregistrement, il est d'usage d'utiliser d'autres types de codes comme, par exemple, le code dit N.R.Z. (non retour à zéro).However, when it is desired to increase the recording density, it is customary to use other types of code such as, for example, the so-called N.R.Z. (not return to zero).

La figure 1 illustre deux types de codes: le code impulsionnel et le code N.R.Z., ce pour un mot binaire arbitraire multibit présentant les états logiques suivants:

  • 01001110110.

On réalise immédiatement, au vu de la figure 1, que le code impulsionnel présente beaucoup plus de transitions que le code de type N.R.Z. Il est alors plus difficile de dériver de ce dernier des informations pour la synchronisation. Sur la figure, la période T représente la durée d'un signal binaire élémentaire ou bit qui correspond à une fréquence de rhytme f=1/T.FIG. 1 illustrates two types of codes: the impulse code and the NRZ code, this for an arbitrary binary multibit word having the following logical states:
  • 01001110110.

It is immediately apparent, in view of FIG. 1, that the pulse code has many more transitions than the NRZ type code. It is therefore more difficult to derive information from the latter for synchronization. In the figure, the period T represents the duration of an elementary binary signal or bit which corresponds to a rhythm frequency f = 1 / T.

Il n'est pas non plus possible d'utiliser une piste annexe réservée à la synchronisation, ce qui détruirait de ce fait le gain en densité permit par le code N.R.Z.It is also not possible to use an annex track reserved for synchronization, which would therefore destroy the gain in density allowed by the code N.R.Z.

Pour pallier les difficultés énoncées, l'invention a pour objet un procédé dont la caractéristique principale est de dériver les signaux nécessaires à la synchronisation de l'écriture et/ou la lecture de données numériques sur un support d'information optique, de données numériques spécifiques ou drapeaux, enregistrés sur la piste commune aux données numériques d'information, mais multiplexées spatialement avec celles-ci.To overcome the difficulties stated, the subject of the invention is a method the main characteristic of which is to derive the signals necessary for synchronizing the writing and / or reading of digital data on an optical information medium, of digital data specific or flags, recorded on the track common to digital information data, but spatially multiplexed with it.

Ces drapeaux peuvent être inscrits préalablement à toute inscription d'informations utiles et sont alors utilisés pour la génération de signaux de synchronisation lors de l'inscription ultérieure de ces informations et lors des lectures successives; ou encore sont multiplexées en temps avec l'inscription de ces informations et sont utilisés lors de la lecture ultérieure de celles-ci.These flags can be registered prior to any registration of useful information and are then used for the generation of synchronization signals during the subsequent registration of this information and during successive readings; or are multiplexed in time with the recording of this information and are used when reading it later.

La figure 2 illustre un exemple d'agencement conforme à l'invention. Sur cette figure a été représenté un tronçon d'une des pistes 91, d'un disque, d'axe moyen 910. Dans l'exemple considéré, il s'agit de pistes de configuration circulaire. Le long de ces pistes sont enregistrés des drapeaux 92 conformément à la caractéristique principale de l'invention.FIG. 2 illustrates an example of an arrangement in accordance with the invention. In this figure has been shown a section of one of the tracks 91, of a disc, of average axis 910. In the example considered, these are tracks of circular configuration. Along these tracks are recorded flags 92 in accordance with the main feature of the invention.

Il est nécessaire que les données numériques spécifiques représentant ces drapeaux soient sélectivement identifiables de manière à ne générer des signaux de synchronisation uniquement en corrélation avec l'apparition de ces drapeaux spécifiques et au contraire qu'ils soient "transparent" pour les circuits de traitement des informations utiles.It is necessary that the specific digital data representing these flags be selectively identifiable so as to generate synchronization signals only in correlation with the appearance of these specific flags and on the contrary that they are "transparent" for the processing circuits of the useful information.

Pour ce faire, si on utilise on code du type N.R.Z. comme représenté sur la partie supérieure de la figure 1, on enregistre des drapeaux spécifiques sous forme d'impulsions dont les intervalles de temps séparant des fronts de même nature sont interdits dans le code de modulation. Pour le code N.R.Z. les durées T et multiples entiers de T sont utilisées. On choisi pour les impulsions spécifiques enregistrées une durée égale à la plus petite durée, demi-entière utilisable c'est à dire 1,5 T.To do this, if we use code of type N.R.Z. as shown in the upper part of FIG. 1, specific flags are recorded in the form of pulses whose time intervals separating fronts of the same kind are prohibited in the modulation code. For code N.R.Z. durations T and integer multiples of T are used. We chose for the specific pulses recorded a duration equal to the smallest duration, usable half-integer ie 1.5 T.

Une telle impulsion est illustrée par le diagramme de la figure 3. Une première partie est au "1" logique pendant l'intervalle de temps égal à 1,5 T, intervalle de temps TA-TB et au "0" logique pendant l'intervalle de temps égale à T: intervalle Ta-Tc.Such a pulse is illustrated by the diagram in FIG. 3. A first part is at logic "1" during the time interval equal to 1.5 T, time interval T A -T B and at logic "0" during the time interval equal to T: interval Ta-Tc.

On peut distinguer deux situations particulières. La première est le cas où le disque est prégravé, c'est à dire comporte les drapeaux, inscrits antérieurement à tout enregistrement de données numériques d'information utile. Dans une variante préférée, l'inscription de ces drapeaux le long des pistes est périodique et les espaces laissés libres entre les drapeaux définis sont des blocs ou des secteurs de données: on peut dans ce cas obtenir un mode de fonctionnement entièrement synchrone.We can distinguish two particular situations. The first is the case where the disc is pre-burned, that is to say contains the flags, registered prior to any recording of digital data of useful information. In a preferred variant, the registration of these flags along the tracks is periodic and the spaces left free between the defined flags are blocks or data sectors: in this case it is possible to obtain a fully synchronous operating mode.

Le second cas est celui où les drapeaux sont inscrits en même temps que l'enregistrement des données numériques d'informations utiles. Comme précédemment, les drapeaux peuvent être inscrits en des sites spécifiques, régulièrement espacés ou non, ou encore être inscrits multiplexés avec les données numériques d'informations utiles.The second case is that where the flags are registered at the same time as the recording of the digital data of useful information. As before, the flags can be registered in specific sites, regularly spaced or not, or even be registered multiplexed with the digital data of useful information.

Le procédé de l'invention selon une variante préférée va maintenant être décrit de façon plus détaillé à l'aide du dispositif représenté par le diagramme synoptique de la figure 4. Des organes optoélectroniques de détection et les circuits électroniques associés 1 fournissent un signal de lecture VL transmis d'une part à des circuits classiques de traitement de l'information lue 6 et, d'autre part, aux circuits spécifiques de la présente invention.The method of the invention according to a preferred variant will now be described in more detail using the device represented by the block diagram of FIG. 4. Optoelectronic detection members and the associated electronic circuits 1 provide a read signal V L transmitted on the one hand to conventional circuits for processing the information read 6 and, on the other hand, to the specific circuits of the present invention.

Selon le procédé de l'invention, il est tout d'abord nécessaire de déterminer si les signaux VL sont issus de la lecture d'informations utiles ou au contraire de la lecture de drapeaux destinés à la synchronisation. Cette étape est réalisée à l'aide de circuits. de détection de drapeaux 2 qui seront détaillés ultérieurement. Ces circuits fournissent un signal d'autorisation VA transmis à des circuits de calcul de déphasage 3. Ces circuits, selon la caractéristique fondamentale de l'invention, ont pour but de fournir des informations A(p représentatives de l'instant d'apparition d'une transition d'un sens déterminé du microrelief défilant sous la tache de lecture. Le signal d'autorisation VA, par exemple après inversion logique VA par l'inverseur 7, peut être utilisé à des fins d'inhibition-autorisation de fonctionnement des circutis de traitement des informations lues 6.According to the method of the invention, it is first of all necessary to determine whether the signals V L come from the reading of useful information or on the contrary from the reading of flags intended for synchronization. This step is carried out using circuits. 2 flags detection which will be detailed later. These circuits supply an authorization signal VA transmitted to phase shift calculation circuits 3. The purpose of these circuits, according to the fundamental characteristic of the invention, is to supply information A (p representative of the time of appearance d 'a transition from a determined direction of the microrelief scrolling under the reading spot. The authorization signal VA, for example after logic inversion VA by the inverter 7, can be used for the purpose of inhibiting-authorizing the operation of the processing circuits for the information read 6.

Le dispositif comporte également des circuits d'horloge 4 générant des impulsions de synchronisation H régénérées par des circuits 5, c'est à dire remis en phase et transmis sous forme d'un signal re-synchronisé Hs aux circuits de traitement de l'information lue. Des circuits d'horloges fournissent également au circuit de calcul de déphasage 3 des signaux d'horloge de référence H, et les signaux H. De façon classique, ces circuits d'horloges comprennent un oscillateur piloté par quartz présentant une grande stabilité.The device also includes clock circuits 4 generating synchronization pulses H regenerated by circuits 5, that is to say re-phased and transmitted in the form of a re-synchronized signal H s to the processing circuits of the information read. Clock circuits also supply to the phase shift calculation circuit 3 reference clock signals H, and the signals H. Conventionally, these clock circuits comprise an oscillator controlled by quartz having great stability.

On admet que la vitesse relative support d'information-tête d'enregistrement ou lecture est définie avec suffisamment de précision suivant une loi reproductible: par exemple vitesse angulaire constant pour un disque.It is assumed that the relative speed of the information carrier, recording or reading head is defined with sufficient precision according to a reproducible law: for example constant angular speed for a disc.

Dans ce cas, pendant les phases de lecture, la fréquence et la phase des signaux de synchronisation Hs sont générés à partir des informations de phase extraites des drapeaux détectés.In this case, during the reading phases, the frequency and the phase of the synchronization signals H s are generated from the phase information extracted from the detected flags.

Dans une configuration de drapeaux périodiques,-on regénère le rythme de bit, c'est à dire la fréquence de l'horloge H à partir du rythme de blocs, c'est à dire au rythme de la détection de drapeaux (passages successifs sous la tête de lecture). Pour ce faire, le signal VA est également transmis aux circuits d'horloge 4.In a configuration of periodic flags, the bit rate is regenerated, that is to say the frequency of the clock H from the block rhythm, that is to say at the rate of the detection of flags (successive passages under the read head). To do this, the signal VA is also transmitted to the clock circuits 4.

La remise en phase par les circuits 5 est effectuée à l'aide des informations Δϕ fournies par les circuits de détection de drapeaux 2.The resetting by the circuits 5 is carried out using the information Δϕ provided by the flag detection circuits 2.

Si, de plus, le rythme de bit des données numériques d'informations utiles lues est très stable, c'est à dire si le glissement de phase par bloc (entre deux passages de drapeaux) est inférieur à une fraction d'élément binaire (glissement en temps inférieur à une fraction déterminée de l'intervalle de temps T) l'opération de regénéra- tion de la fréquence n'est pas nécessaire.If, moreover, the bit rate of the digital data of useful information read is very stable, that is to say if the phase shift per block (between two passages of flags) is less than a fraction of binary element ( slip in time less than a determined fraction of the time interval T) the frequency regeneration operation is not necessary.

Ceci peut être obtenu en asservissant la vitesse relative support-tête d'enregistremenf et/ou lecture par des moyens qui sortent du cadre de la présente invention.This can be obtained by slaving the relative support-head speed of recording and / or reading by means which are outside the scope of the present invention.

Dans ce cas, le dispositif de l'invention se réduit aux circuits simplifiés illustrés sur la figure 5. Il n'y a plus de circuits de détection de drapeaux (fig. 4:2), la position de ceux-ci étant connue. Les signaux d'autorisation-inhibition peuvent être dérivés des signaux d'horloge, respectivement HA et via l'inverseur 8: HA. Les autres circuits sont identiques à ceux de la figure 4 et ne seront pas décrits à nouveau.In this case, the device of the invention is reduced to the simplified circuits illustrated in FIG. 5. There are no longer flag detection circuits (fig. 4: 2), the position of these being known. The authorization-inhibition signals can be derived from the clock signals, respectively H A and via the inverter 8: H A. The other circuits are identical to those of FIG. 4 and will not be described again.

Les différents circuits des dispositifs des figures 5 et/ou 4 vont maintenant être décrits de façon plus détaillée.The different circuits of the devices of FIGS. 5 and / or 4 will now be described in more detail.

Un exemple de circuit de détection de drapeaux et de détermination de l'instant de passage d'un drapeau sous la tache de lecture est illustré par la figure 6. Ce circuit comprend un premier circuit 20 de mise en forme du signal lu VL- Il peut être constitué de façon avantageuse par un élément bistable comparant un signal lu VL à une tension de seuil VSEUIL fournissant une impulsion VLS, par exemple, à un état logique "1" lorsque le signal lu dépasse le seuil et à l'état "0" dans le cas contraire. Ce signal VLs est transmis à un circuit 21 destiné à générer un signal impulsionnel définissant une fenêtre de temps VF.An example of a circuit for detecting flags and determining the instant when a flag passes under the reading spot is illustrated in FIG. 6. This circuit comprises a first circuit 20 for shaping the signal read V L - It can advantageously consist of a bistable element comparing a read signal V L with a threshold voltage V THRESHOLD supplying a pulse V LS , for example, in a logic state "1" when the signal read exceeds the threshold and with l 'state "0" otherwise. This signal V Ls is transmitted to a circuit 21 intended to generate a pulse signal defining a time window V F.

Ces signaux sont illustrés par le diagramme de la figure 8. La courbe H représente des impulsions fournies par les circuits d'horloge 4 de durée de base T. Le signal impulsionnel VLS peut présenter un déphasage par rapport aux signaux d'horloges quelconque modulo la période de ces signaux.These signals are illustrated by the diagram in FIG. 8. The curve H represents pulses supplied by the clock circuits 4 of basic duration T. The pulse signal V LS can have a phase shift with respect to any clock signals modulo the period of these signals.

Le circuit 21 est déclenché par le font montant de la première impulsion de drapeau, à l'instant TA sur le diagramme, et délivre une impulsion VF dont le centre est retardé de 1,5 T. Pour ce faire on peut utiliser deux bascules monostables géné- rants des impulsions de durées respectivement un peu supérieures et un peu inférieures à 1,5 T. L'intersection logique de ces deux impulsions peut être utilisée pour déterminer la fenêtre de temps VF.Circuit 21 is triggered by the rising amount of the first flag pulse, at time T A on the diagram, and delivers a pulse VF whose center is delayed by 1.5 T. To do this, two flip-flops can be used monostable generating pulses of durations respectively slightly greater and slightly less than 1.5 T. The logical intersection of these two pulses can be used to determine the time window V F.

L'information de déphasage Δϕ peut s'obtenir par comparaison avec un instant déterminé de la période du signal d'horloge de base H, de manière numérique ou analogique. Le signal Δϕ produit par les circuits de calcul de déphasage peut se présenter sous la forme d'un signal impulsionnel présentant une transition d'un sens déterminé dont l'instant d'apparition est représentatif du déphasage du drapeau par rapport à un instant prédéterminé des signaux d'horloge H ou un mot binaire d'adresse définissant le déphasage.The phase shift information Δϕ can be obtained by comparison with a determined instant of the period of the basic clock signal H, digitally or analogically. The signal Δϕ produced by the phase shift calculation circuits can be in the form of a pulse signal having a transition of a determined direction whose time of appearance is representative of the phase shift of the flag with respect to a predetermined time of the H clock signals or a binary address word defining the phase shift.

Dans une variante de réalisation préférée, on utilise le signal d'horloge H et un signal d'horloge HR de fréquence multiple de la fréquence de répétition du signal d'horloge de base H et en relation de phase fixe avec ce signal. Le second signal d'horloge peut être dérivé de façon aisée du signal H à l'aide d'un multiplicateur de fréquence. A titre d'exemple, sur le diagramme de la figure 8, le signal d'horloge HR a une fréquence de répétition seize fois plus grande que celle du signal H. Il définit donc seize sous-intervalles. Un circuit décodeur peut fournir un mot binaire Δϕ représentant le décalage de l'instant TB par rapport à un instant de référence fixe de la période du signal d'horloge de base H, ce modulo seize. Le mot binaire Δϕ ou mot de commande sert à la remise en phase, à chaque passage de drapeau, du signal d'horloge utilisé comme signal de synchronisation Hs. Ce signal peut servir lors de la lecture de données numériques d'informations utiles entre les passages successifs de deux drapeaux, soit, lorsque ces drapeaux sont inscrits préalablement à l'enregistrement de données, sous forme de prégravures, également pour l'écriture de ces données.In a preferred embodiment, the clock signal H and a clock signal H R of frequency multiple of the repetition frequency of the basic clock signal H and in fixed phase relation with this signal are used. The second clock signal can be easily derived from the H signal using a frequency multiplier. By way of example, in the diagram of FIG. 8, the clock signal H R has a repetition frequency sixteen times greater than that of the signal H. It therefore defines sixteen sub-intervals. A decoder circuit can supply a binary word Δϕ representing the offset of the instant T B with respect to a fixed reference instant of the period of the basic clock signal H, this modulo sixteen. The binary word Δϕ or control word is used to reset the clock signal used as synchronization signal H s with each passing of the flag. This signal can be used during the reading of digital data of useful information between the successive passages of two flags, that is to say, when these flags are registered before the recording of data, in the form of pre-engravings, also for the writing of these data.

Les nouveaux signaux d'horloge regénérés doivent être en relation de phase constante avec le passage des drapeaux, c'est à dire par exemple avec l'instant TB front descendant de l'impulsion de drapeau tel qu'il vient d'être déterminé. Les signaux de synchronisation Hs ont même fréquence que les signaux d'horloge H et une relation de phase dépendant de la valeur du mot de commande Δϕ.The new regenerated clock signals must be in constant phase relation with the passage of the flags, that is to say for example with the instant T B falling edge of the flag pulse as it has just been determined. . The synchronization signals H s have the same frequency as the clock signals H and a phase relationship depending on the value of the control word Δϕ.

Un exemple de réalisation des circuits d'horloge est représenté sur la figure 7. Ces circuits comprennent un oscillateur classique piloté par quartz, du type contrôlé par la tension ("V.C.O.") muni d'une boucle de retroaction à verrouillage de phase ("P.L.L.") comportant en série un diviseur 41 de fréquence par un nombre déterminé N, un comparateur de phase 42 recevant sur une première entrée la sortie du diviseur 41 et sur une seconde entrée les signaux VA issus du détecteur de drapeau 2 et un filtre passe-bas 43. La fréquence de sortie H de l'oscillateur est asservie sur un multiple N du rythme de passage des drapeaux . sous la tache de lecture.An exemplary embodiment of the clock circuits is shown in FIG. 7. These circuits include a conventional quartz-controlled oscillator, of the voltage-controlled type ("VCO") provided with a phase-locked feedback loop (" PLL ") comprising in series a frequency divider 41 by a determined number N, a phase comparator 42 receiving on a first input the output of the divider 41 and on a second input the signals VA coming from the flag detector 2 and a low-pass filter 43. The output frequency H of the oscillator is controlled on a multiple N of the rate at which flags pass. under the reading spot.

L'oscillateur qui vient d'être décrit s'applique plus particulièrement aux circuits illustrés par la figure 4. Lorsque les circuits de la figure 5 sont mis en oeuvre l'oscillateur peut être réduit à sa plus simple expression, la comparaison de phase n'étant plus nécessaire.The oscillator which has just been described applies more particularly to the circuits illustrated in FIG. 4. When the circuits of FIG. 5 are implemented, the oscillator can be reduced to its simplest expression, the phase comparison n being no longer necessary.

Enfin, un signal d'horloge H, de fréquence multiple du signal d'horloge de base H peut être généré à partir de ce dernier à l'aide d'un multiplicateur de fréquence 44.Finally, a clock signal H, of frequency multiple of the basic clock signal H can be generated from the latter using a frequency multiplier 44.

Les circuits de remise en phase 5 peuvent comprendre également un oscillateur commandé en tension muni d'une boucle à verrouillage de phase du type de celui qui vient d'être décrit piloté en fréquence par les signaux d'horloge H ou une ligne à retard programmable. Le recalage en phase sur les drapeaux est fait à l'aide du signal de commande Δϕ.The phase-resetting circuits 5 can also include a voltage-controlled oscillator provided with a phase-locked loop of the type which has just been described, controlled in frequency by the clock signals H or a programmable delay line . The phase adjustment on the flags is done using the control signal Δϕ.

La présente invention peut être mise en oeuvre dans de nombreux appareils écriture-lecture par voie optique de support d'information et à titre d'exemple la figure 9 illustre de façon schématique, un appareil d'enregistrement-lecture sur un support par voie optique dans lequel le procédé de la présente invention peut être mis en oeuvre. Un disque 90 tournant dans un plan XOY autour d'un axe parallèle au troisième axé Z du triède de référence XYZ comporte sur sa face supérieure une couche de matériau thermo-sensible dans laquelle des informations ont été enregistrées le long des pistes 91. Ces pistes comportent également des drapeaux 92 associés à un code spécifique conformément à ce qui a été décrit. Les données numériques d'informations utiles sont enregistrées entre ces drapeaux dans des zones 93, de préférence de longueur constante. Le disque, d'un diamètre d'environ 30 cm, est animé d'un mouvement de rotation communiqué par un moteur d'entrainement solidaire du chassis du système optique d'enregistrement-lecture. De façon typique, les pistes au nombre par exemple de 40 000 sont inscrites à l'intérieur d'une couronne centrée sur l'axe de rotation et de largeur égale à environ 8 cm. Le nombre de drapeaux inscrits par pistes circulaires concentriques doit être suffisant pour s'affranchir de phénomènes parasites liés à la nature du support ou à la fluctuation de la vitesse de rotation. Typiquement on inscrit 3 500 drapeaux par pistes, compte-tenu des données précédentes.The present invention can be implemented in numerous writing-reading apparatuses optically by means of an information medium and, by way of example, FIG. 9 schematically illustrates a recording-reading apparatus on a medium by optical means in which the method of the present invention can be implemented. A disk 90 rotating in a plane XOY around an axis parallel to the third axis Z of the reference triede XYZ has on its upper face a layer of heat-sensitive material in which information has been recorded along the tracks 91. These tracks also include flags 92 associated with a specific code in accordance with what has been described. The useful information digital data is recorded between these flags in zones 93, preferably of constant length. The disc, with a diameter of about 30 cm, is driven by a rotational movement communicated by a drive motor secured to the chassis of the optical recording-reading system. Typically, the tracks, for example 40,000 in number, are inscribed inside a crown centered on the axis of rotation and of width equal to approximately 8 cm. The number of flags registered per concentric circular tracks must be sufficient to overcome parasitic phenomena related to the nature of the support or to the fluctuation of the speed of rotation. Typically 3,500 flags are entered per runway, taking into account the previous data.

Dans l'exemple de réalisation illustré par la figure 9, le dispositif d'accès à une piste prédéterminée du disque comprend une partie fixe comportant une source d'énergie (non-représentée) générant un faisceau de rayons parallèles f et une partie mobile constituée par la tête d'enregistrement-lecture proprement dite. Comme il est connu, cette dernière comprend un objectif du type microscope Ob, solidaire d'une bobine électromagnétique B se déplaçant dans le champ magnétique d'un aimant permanent (non-représenté) assurant l'asservissement vertical ou focalisation et un miroir galvanométrique M1 assurant l'asservissement radial. Le miroir galvanométrique M1 est mobile autour d'un axe Ay parallèle à l'axe OY du triède de référence de manière à assurer ledit asservissement radial. Le faisceau f est focalisé en une tacheta en un endroit déterminé du disque sur une des pistes 91 précitées. On suppose ici que le système est du type monofaisceau-monopiste, c'est à dire un système dans lequel le faisceau unique f sert alternativement à l'écriture et à la lecture ainsi que pour assurer les fonctions de suivi radial de piste et de focalisation. Cet aspect sort du cadre de l'invention.In the embodiment illustrated in FIG. 9, the device for accessing a predetermined track of the disc comprises a fixed part comprising an energy source (not shown) generating a beam of parallel rays f and a mobile part constituted by the recording-playback head itself. As is known, the latter comprises a microscope type objective O b , integral with an electromagnetic coil B moving in the magnetic field of a permanent magnet (not shown) ensuring vertical servo-control or focusing and a galvanometric mirror M 1 ensuring the radial control. The galvanometric mirror M 1 is movable around an axis Ay parallel to the axis OY of the reference triede so as to ensure said radial control. The beam f is focused in a tacheta at a determined location on the disc on one of the tracks 91 mentioned above. It is assumed here that the system is of the single-beam-single track type, that is to say a system in which the single beam f is used alternately for writing and reading as well as for ensuring the functions of radial tracking of track and focusing. . This aspect is outside the scope of the invention.

Pour détecter le faisceau de lecture réfléchi par le disque, on interpose, par exemple, une lame semi-transparente M2 sur le trajet du faisceau unique f. Le faisceau réfléchi par le disque est alors détecté par des moyens photodétecteurs D qui génèrent le signal VL à des circuits 94 de traitement de ce signal. Ces circuits comprennent notamment des circuits propres à l'invention, par exemple le dispositif décrit en relation avec la figure 7.To detect the reading beam reflected by the disc, a semi-transparent plate M 2 is interposed, for example, on the path of the single beam f. The beam reflected by the disc is then detected by photodetector means D which generate the signal V L to circuits 94 for processing this signal. These circuits include in particular circuits specific to the invention, for example the device described in relation to FIG. 7.

L'invention est également compatible avec les appareils d'enregistrement-lecture mettant en oeuvre plus d'un faisceau par exemple un faisceau de lecture et un faisceau d'écriture.The invention is also compatible with recording-reading apparatuses using more than one beam, for example a reading beam and a writing beam.

En résumé, le procédé de l'invention permet, entre autres avantages, de tirer partie de l'indépendance qui existe entre le codage des données numériques représentant l'information et la synchronisation ainsi qu'une moins grande dépendance vis à vis des pertes d'informations dues à des "blancs" en lecture plus connus sous la dénomination anglo-saxonne de "dropouts".In summary, the method of the invention makes it possible, among other advantages, to take advantage of the independence which exists between the coding of digital data representing the information and the synchronization as well as a less dependence with respect to the losses of information due to "blanks" in reading better known by the Anglo-Saxon name of "dropouts".

Claims (18)

1. A method of generating sync signals (Hs) in an apparatus for the optical transcription of digital data onto a substrate (90) performing an exploratory motion; said data being recorded in the form of perturbations (92) in at least one layer of material of the substrate and able to be optically detected along tracks (91) of a given configuration, the said tracks comprising a succession of noncontiguous sites intended for storing the said data between which there are placed interstitial sites intended for another form of use the said device comprising means for focusing at an exploration spot (ta), at least one beam (f) of light energy on the one of the said tracks, optoelectronic means (1) for the detection of the interaction of this beam with the said perturbations moving past under the exploration spot and selector means (2) connected with these optoelectronic means in order to provide a signal which is characteristic of the content of the said interstitial sites, said method being characterized in that it comprises the following stages:
-the writing exclusively in the said interstitial sites of specific digital data (92) in the form of a sequence of perturbations of the said layer of material producing transitions playing a reference part in relation to the said sync signals but whose differences are able to be seen from those used for the transcription of the said digital data;
-the local generation of a signal, external of the substrate, such signal being a periodic clock signal (H) comprising an element defining a reference instant to be placed in relation to the transcription of the said data;
-the selective identification of specific digital data by the said selector means (2);
-determination by the said selector means of the reference instant (Tg) resulting from the exploration of a transition whose selection is brought about with a given delay in relation to another transition; the said transition and the other transition being produced, at least one of them, by the same perturbation included in the said specific digital data (92) in response to the exploration by the said spot (ta) of the said interstitial sites; the said delay being dependent on the estimated duration existing between these two transitions;
-determination of the offset of this reference instant (T a) with respect to the true reference instant of the said periodic clock signal (H); and the generation of the said sync signal (Hs) starting from the said periodic clock signal (H) corrected by the said offset.
2. The method as claimed in claim 1, characterized in that the digital data subjected to the said recording generate transitions whose separations are characteristic for the modulation code utilized; the said specific digital data being composed of perturbations which generate a set of transitions having, in relation to these characteristic separations, the exclusive property of being identifiable by the said selector means (2).
3. The method as claimed in claim 2, characterized in that, the said modulation code having separations of a duration T and entire multiples thereof, the said set of transitions comprises intervals of time between flanks composed of half a complete duration T/2 and at least one entire duration T; the said flanks of the same nature being forbidden in the said modulation code.
4. The method as claimed in any one of the claims 1 through 3, characterized in that the stage of determining the reference instance of a said interstitial site in the exploratory spot is effected by the detection of the instant (Ta) of the appearance of a transition of a predetermined direction of one of the pulses of the specific digital data.
5. The method as claimed in claim 3, characterized in that the stage of identification and of determination of the reference instant are merged in a single stage and in that a time window (VF) is generated initialized by the first transition in a first direction of one of the specific digital data pulses and delayed by one time interval equal to one and a half times the said determined elementary value T, and the logic intersection is effected of this time window with the said pulses in order to conditionally generate a pulse (VA) making it possible to determine the said passage instant (Tg).
6. The method as claimed in-any one of the claims 1 through 5, characterized in that writing during the preliminary phase of specific digital data is effected prior to the writing all the digital information data on the said substrate and in that the said sync signals (Hs) are utilized in the later phases for the writing and reading of these digital information data.
7. The method as claimed in any one of the claims 1 through 6, characterized in that the said specific digital data are written at sites (92) which are regularly spaced along the tracks (91) which between them define these sites of blocks (93) reserved for the writing of the digital information data.
8. A device for the generation of sync signals for an apparatus for the optical transcription of digital data on a substrate (90) caused to perform an exploratory motion; the said data being recorded in the form of perturbations (92) of at least one layer of material able to be optically detected along tracks (91) of a predetermined configuration; the said tracks comprising a succession of noncontiguous sites intended for the storage of the said data between there are interstitial sites intended for another purpose; said device comprising selector means connected with optoelectronic means detecting the optical interaction produced at the time of motion of one of the said tracks past an optical exploratory spot, the said selector means supplying a signal characteristic of the content of the said interstitial sites which exerts an action on setting means (5) supplying said sync signals, characterized in that it comprises means (4) for the local generation outside the substrate of reference signals and periodic clock signals connected with the said setting means (5) and with a first input of the dephasing computing means (3); the said dephasing computing means receiving via a second input a reference signal provided by the said selector means (2) upon each identification of an interstitial site and producing dephasing information corresponding to the dephasing of the reference signals originating from the means (4) for the local generation of periodic clock signals and selector means (2); the said dephasing information being taken into account by the said setting means so that the said sync signals permit the writing or the reading in a chronological order of the digital data whose transcription is commenced after the identification of the said interstitial site by the specific transitions contained by it.
9. The device as claimed in claim 8, characterized in that the specific digital data comprise at least two transitions whose distance apart is forbidden in the modulation code of the digital data, the said selector means (2) comprising a detector for said transitions receiving output signals (VL) of the said photoelectric means and comprising a time window (VF) generator (21) initialized by the said first of said transitions to be received; the said time window (VF) comprising two specifically retarded transitions in order to frame in and isolate the second of the said transitions received; the extraction of the said isolated transition being performed by a logical coincidence gate (22) which furnishes one of the time references needed for the dephasing computing means (3).
10. The device as claimed in any one of the claims 8 and 9, characterized in that the interstitial site containing the said specific digital data comprises at least two pulses whose transitions of the same nature are forbidden in the modulation code of the digital data.
11. The device as claimed in any one of the claims 8 through 10, characterized in that the means (4) for the local generation of reference signals and periodic clock signals comprise a voltage controlled oscillator (V.C.O.) provided with a phase locked loop (P.L.L.) in order to lock its frequency to a multiple of the rhythm of the identification signal provided by the said selector means (2).
12. The method as claimed in any one of the claims 1 through 7, characterized in that it comprises a supplementary stage consisting in setting the frequency of the said periodic clock signal (H) in accordance with the rate of appearance of the reference instant (TB).
13. An information carrying substrate intended for use in the method as claimed in any one of the claims 1 through 7 and 12, of the type comprising an array of adjacent tracks placed in a reference surface, along which there is provided a succession of noncontiguous sites intended for the storage of digital data, between which there are placed interstitial sites comprising specific digital data intended for another use, characterized in that the transcription of the digital data from and to the substrate is controlled by a periodic sync signal exclusively transcribed by a submultiple of its true frequency by means of the said interstitial sites, which contain a sequence of optically detectable perturbations producing transitions playing the role of a reference in relation to the said periodic sync signal, but whose separation is discernible by those used for the transcription of the said digital data.
14. The substrate as claimed in claim 13, characterized in that the said digital data subjected to transcription generate transitions whose separation is characteristic for the modulation code used; the said modulation code having separations of a duration T and entire multiples of T; the set of transitions contained in the said interstitial sites comprising time intervals between flanks composed of a semi-entire duration equal to T/2 and at least an entire duration T; the said flanks of the same nature being forbidden in the said modulation code.
15. The substrate as claimed in any one of the claims 13 and 14, characterized in that the transcription of the said specific digital data in the said interstitial sites constitutes a preliminary to each transcription of digital data in the sites intended for this transcription.
16. The substrate as claimed in any one of the claims 13 through 15, characterized in that the interstitial sites are regularly spaced out along the said tracks.
17. The substrate as claimed in any one of the claims 13 through 16, characterized in that the each interstitial site comprises at least two pulses.
18. The substrate as claimed in any one of the claims 13 through 17, characterized in that the interstitial sites are pre-engraved and in that the digital data are transcribed in a sensitive ther- mooptic structure comprising at least one recording layer causing the appearance of the pre-engraving of the said interstitial sites.
EP83400428A 1982-03-12 1983-03-02 Method and device for generating synchronizing signals in an optical recording-reproducing apparatus for record carriers Expired EP0089264B1 (en)

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FR2523345A1 (en) 1983-09-16
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US4566092A (en) 1986-01-21
JPH08339633A (en) 1996-12-24
FR2523345B1 (en) 1984-04-20

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